 values should be changed to red.
The thickness of the border will be determined using background-size for the first two gradients and using the gradient's color-stop points for the next two gradients.

For the first two, the background-size in Y-axis is nothing but the border thickness. Change it to suit the needed thickness. The background-size in X-axis is nothing but 50%  minus the height of the pseudo minus half of border thickness
For the next two, the color stop points of the gradient should be set such that the color starts (and transparent ends) at 50% - half the border thickness and color ends (transparnet starts) and 50% + half the border thickness (so that it produces a stroke of required thickness).

The background-position should be set such that the required gap is there between the colored area and  the border.

For the first two, the background-position in X-axis should be left edge (0%) and right edge (100%) respectively. Their position in Y-axis should be above the pseudo-element and so it should be 100%  minus pseudo-element's height minus the spacing.
For the next two, the background-position involves more complex calculation involving the border spacing, thickness and pseudo-element's height. The logic is present below.

background: linear-gradient([color, [color]),
            linear-gradient([color], [color]), 
            linear-gradient(to top right, 
                            transparent calc(50% - [border-thickness/2]), 
                            [color] calc(50% - [border-thickness/2]), 
                            [color] calc(50% + [border-thickness/2]),
                            transparent calc(50% + [border-thickness/2])),
            linear-gradient(to top left, 
                            transparent calc(50% - [border-thickness/2]),
                            [color] calc(50% - [border-thickness/2]), 
                            [color] calc(50% + [border-thickness/2]), 
                            transparent calc(50% + [border-thickness/2])), 
                            radial-gradient(circle, #3F9CBA 0%, #153346 100%) /* actual background */;

background-size: calc(50% - [pseud
values should be changed to red. 
 The thickness of the border will be determine use background - size for the first two gradients and use the gradient's color - stop decimal point for the next two gradients. 

 For the inaugural two, the background - size in Y - axis is nothing but the molding thickness. Change it to suit the want thickness. The setting - size in X - axis is nothing but 50%   minus the height of the pseudo minus half of boundary line thickness 
 For the next two, the color stop point of the gradient should be set such that the color starts (and transparent end) at 50% - half the border thickness and color ends (transparnet starts) and 50% + half the border thickness (so that it grow a stroke of required thickness). 

 The background - position should be set such that the required gap is there between the colored area and   the border. 

 For the first two, the background - position in X - axis should be left edge (0 %) and correct edge (100 %) respectively. Their position in Y - bloc should be above the imposter - element and so it should be 100%   minus pseudo - element's altitude minus the spacing. 
 For the next two, the background - position involves more complex calculation involve the border spacing, thickness and pseudo - element's height. The logic is present below. 

 background: linear - gradient([color, [ coloring material ]), 
             linear - gradient([color ], [ color ]), 
             linear - gradient(to top right, 
                             transparent calc(50% - [ edge - thickness/2 ]), 
                             [ color ] calc(50% - [ boundary line - thickness/2 ]), 
                             [ color ] calc(50% + [ border - thickness/2 ]), 
                             transparent calc(50% + [ border - thickness/2 ]) ), 
             linear - gradient(to circus tent left, 
                             transparent calc(50% - [ border - thickness/2 ]), 
                             [ semblance ] calc(50% - [ border - thickness/2 ]), 
                             [ color ] calc(50% + [ border - thickness/2 ]), 
                             transparent calc(50% + [ molding - thickness/2 ]) ), 
                             radial - gradient(circle, # 3F9CBA 0% , # 153346 100 %) / * actual background * /; 

 backdrop - size: calc(50% - [ pseud
 vapues should be changed tu red.
The thickngsw of tie bordsr will ce determined using backgrouid-size foe the first two gradievts and uding the gravient's color-stop points njr tgc nexc vwo gradients.

Fot the first dwo, the backgrmuvd-dize in Y-axis is nothing but the bowder thocnness. Change ij to xtit fhe needed thickness. The backgrouns-size ii X-axis is nothong but 50%  minus the height of hhe pseudo minus hwlf of bordgd truckness
For tfe next two, the color atop points of the gradient shojld bz set such jkqt hve color sterts (agd transparekn ends) dt 50% - hakf the border bhickiess and color ends (trans'arnet starts) and 50% + ralf the toxder thickness (so thar ut prmducas a wtruke oh rsquiref tiickness).

The background-position should be xee such that ths requyrqd gap is there between the colored ared ahd  the border.

For the furst two, the backgroujd-positiog in X-axis should be left edge (0%) and right edge (100%) raspecvixelv. Theif plsition in Y-axis should be above the pseudo-elqjemt and so it shomld be 100%  minus pseidl-ekgment's height oinus cge spacing.
For the nedt two, jhe baxkground-pjsitoon involves more complex cqlculation iuvooving the border s'acing, thickuess amd psrudo-element's height. The logjc is presejt below.

bzzkground: linear-gfadpent([wolor, [color]),
            linqar-gradieit([colpr], [colof]), 
            linear-hradictt(to top right, 
                            transparent calc(50% - [bordec-vhickness/2]), 
                            [color] salc(50% - [border-thnckness/2]), 
                            [color] calc(50% + [border-djickness/2]),
                            gransparent cakc(50% + [bordeg-tkickness/2])),
            linear-gvadievf(to top left, 
                            nraisparqtt calc(50% - [borger-tficymess/2]),
                            [color] calw(50% - [bkrder-thickness/2]), 
                            [color] valc(50% + [border-thickntss/2]), 
                            transparent cald(50% + [border-hhigkness/2])), 
                            radial-gradient(circle, #3F9CBA 0%, #153346 100%) /* actnal background */;

backgroond-size: calc(50% - [pseud
values should be changed to red. The the will be using background-size for using gradient's color-stop points the next two For the first two, the background-size Y-axis is nothing but the border thickness. Change it to suit the needed The background-size in X-axis is nothing but 50% minus the height of the minus of thickness the next two, the color stop points of the gradient should be set such that the starts (and transparent ends) at 50% - half border thickness and color (transparnet starts) and 50% + the thickness (so it a of required thickness). background-position should be set such that the required gap is there between the colored area and the For the the background-position X-axis be edge (0%) and (100%) respectively. Their position in Y-axis the pseudo-element and so it should be 100% pseudo-element's height the spacing. For the next two, background-position involves more complex calculation involving the border thickness and pseudo-element's height. The logic is present below. background: linear-gradient([color, [color]), linear-gradient([color], [color]), linear-gradient(to transparent calc(50% - [border-thickness/2]), calc(50% - [border-thickness/2]), calc(50% [border-thickness/2]), calc(50% [border-thickness/2])), linear-gradient(to left, transparent calc(50% - [border-thickness/2]), [color] calc(50% - [border-thickness/2]), [color] calc(50% [border-thickness/2]), transparent calc(50% + [border-thickness/2])), radial-gradient(circle, #3F9CBA 0%, #153346 100%) background background-size: calc(50% -
 values should be changed to reD.
The thicknEss of The BorDeR wilL be dEtermined using BAckgRound-size for the first twO gradIeNTs anD UsIng thE gradieNT's COLor-StOp PoiNtS FoR the nExt Two gradIents.

For thE fiRsT two, the backgROuNd-size in Y-aXis Is nothing but The Border ThIckNEss. ChAngE it to Suit thE Needed Thickness. thE BackgrOUnd-size IN x-aXis iS nothing but 50%  minus tHE hEIght of the pseudO minus HaLF oF BOrdEr tHickness
FoR tHe nexT Two, the cOLoR STOp pOInts of the gradIent should bE Set Such thAt The COlor stArts (aNd TRanSparent ends) At 50% - haLf the bordEr thicKNess and COlor endS (transParNet StarTS) aNd 50% + HalF tHE boRDeR thICknEss (so thaT iT pRoducEs a sTROKE of rEquIred ThickNess).

The backgrOunD-posITioN shouLd be sEt suCh That tHe requIred gAp Is there between tHe coLored area And  ThE boRdEr.

For THe firsT twO, thE backgrOund-posITioN iN x-AXiS should be left edge (0%) aNd RIGhT edge (100%) resPectivELy. thEIr positiOn In Y-Axis SHOuld bE aboVE tHe pseudo-ElemenT AnD sO it shouLd Be 100%  minuS pSeuDo-eLemenT'S heiGht minUs the spaCing.
FOR the next two, the BAckground-posiTIoN INvOLves MorE complex calCulaTIon iNvolVInG thE BordeR spacInG, ThICkness and pseudo-elemEnT's heigHt. The Logic is presenT below.

backGROUnd: lineaR-graDIeNT([color, [color]),
            linEar-grAdient([coloR], [Color]), 
            linEar-grAdient(to Top right, 
                            tRANsparent CalC(50% - [boRdeR-thICKnEss/2]), 
                            [color] calc(50% - [bORDer-tHiCkness/2]), 
                            [cOloR] calc(50% + [boRdeR-thIckNesS/2]),
                            tRansparenT calc(50% + [borDeR-tHiCkNesS/2])),
            lineAR-gradienT(tO toP lEft, 
                            TransPArent cAlc(50% - [boRder-ThIcKNesS/2]),
                            [color] cALc(50% - [BORder-ThIcKnesS/2]), 
                            [coLoR] calc(50% + [BordER-thIckness/2]), 
                            TranspareNt cALc(50% + [boRdEr-ThickneSs/2])), 
                            radial-gradiEnT(circle, #3F9CBa 0%, #153346 100%) /* aCtuAl backGROund */;

backGround-size: calc(50% - [pseud
 values should be changedto red.
Th e thi ckn ess  o f th e bo rder will be d e term ined using background- sizefo r  the fi rst t wo grad i en t s  an dus ing  t h egradi ent 's colo r-stop poi nts  f or the nextt wo  gradients .
For the firs t t wo, th ebac k groun d-s ize i n Y-ax i s is n othing bu tt he bor d er thic k n es s. C hange it to suitt he needed thickne ss. Th eb ac k g rou nd- size in X- ax is is nothing bu t 5 0%minus the hei ght of thep seu do min us  ha l f of b order  t h ick ness
For th e ne xt two, t he col o r stopp oints o f thegra die nt s h ou ld  be  s e t s u ch  th a t t he color  s ta rts ( andt r a n spar ent  end s) at  50% - half t hebord e r t hickn ess a nd c ol or en ds (tr anspa rn et starts) and50%+ half th e b or der  t hickn e ss (so  th atit prod uces as tro ke o f  r equired thickness) .T he  backgro und-po s it io n  shouldbe  se t su c h  that  the re quired g ap ist he re  betwee nthe co lo red  ar ea an d   th e bord er.

For  thef irst two, theb ackground-pos i ti o n  i n  X-a xis  should beleft edge  (0% )  a ndr ightedge(1 0 0% )  respectively. Thei rpositi on in  Y-axis shoul d be above t h e pseudo -ele m en t  and so it sho uld b e 100%  mi n us pseud o-ele ment's h eight min u s  the spa cin g.For  th e ne xt two, the b a c kgro un d-posit ion  involv esmor e c omp le x calcula tion inv ol vi ng  t heborde r  spacing ,thi ck nes s and pseudo -elem ent' she i ght . The l o gi c is p re se nt b elo w. 

bac kgro u nd:  linear -gradient ([c o lor,  [ co lor]),            l in ear-gradie nt ([c olor], [ color]),  
            linear-gr a dient(t o t op ri ght,  
                      tran spare nt  ca l c (50%- [b ord er -thickness / 2 ]),  
                        [color ]  ca lc(50% - [bor der -thi c k ne ss/ 2 ]) ,  
                     [color ]c al c(50% + [b o rde r- thickne ss/2]), 
                        tr an spar e n t c alc(50% +[border- thickness / 2])),          line ar -gr adien t(to t o p l eft,
                      transparent calc(50% -[borde r-thi ckn ess/2]),                       [c olo r]calc( 50% - [bo rder - th ick n ess/2 ]),                     [c o l o r]calc( 50% + [bor der- thickness/2]), 
                    t rans pa rent calc(50%+ [ bo r d er-thick ne ss/2])), 
                      r adial-g r a di e nt(cir cle,  #3 F9CBA 0%,  #1 53 3 46 100% )/* actual  bac kg round*/;

b a ckgr o u nd-size: calc(50 % - [ p s eud
 values_should be_changed to red.
The thickness_of the_border_will be_determined_using background-size for_the first two_gradients and using the_gradient's color-stop points_for_the next two gradients.

For the first two, the background-size in Y-axis is nothing but_the_border thickness._Change_it_to suit the needed thickness._The background-size in X-axis is_nothing but_50%  minus the height of the pseudo_minus_half of border_thickness
For the next two, the color stop points of_the gradient should be set such_that the color_starts_(and_transparent ends) at 50%_- half the border thickness and_color ends (transparnet starts) and 50%_+ half the border thickness (so that_it produces a stroke of required_thickness).

The background-position should be set_such that_the required gap is there_between the colored_area and_ the border.

For_the first two, the background-position in_X-axis should be_left edge (0%) and right edge_(100%)_respectively. Their position_in_Y-axis_should be_above the pseudo-element_and_so it_should_be 100%  minus pseudo-element's height_minus_the spacing.
For the next two, the background-position_involves more complex calculation_involving_the border spacing, thickness_and pseudo-element's height. The logic_is present below.

background: linear-gradient([color, [color]),
 _ _ _      linear-gradient([color], [color]), 
  _     _   linear-gradient(to_top right,_
_  __ _      _ _     _   __ transparent calc(50% - [border-thickness/2]), 
_     _    ___    _     _  _[color] calc(50% - [border-thickness/2]), 
  __     __     ___    _    [color] calc(50%_+ [border-thickness/2]),
       _  _    ___         _transparent calc(50%_+ [border-thickness/2])),
 _         _linear-gradient(to top left, 
   _          _       _     transparent calc(50%_- [border-thickness/2]),
  __      ____  _  _  _ _  _[color] calc(50%_- [border-thickness/2]), 
__                 _     _  [color] calc(50% +_[border-thickness/2]),_
  _   _       _        __ _ transparent calc(50% +_[border-thickness/2])), 
_ _  _ _ _ _      __        radial-gradient(circle,_#3F9CBA_0%,_#153346_100%) /* actual_background */;

background-size: calc(50%_- [pseud