code: def plot_univariate(
      df,
      x_col,
      y_col,
      xlabel=None,
      ylabel=None,
      title=None,
      color="rgb(32, 149, 212)",  # light blue
      showlegend=True,
  ):
      """Simple plot of univariate timeseries.
  
      Parameters
      ----------
      df : `pandas.DataFrame`
          Data frame with ``x_col`` and ``y_col``
      x_col: `str`
          x-axis column name, usually the time column
      y_col: `str`
          y-axis column name, the value the plot
      xlabel : `str` or None, default None
          x-axis label
      ylabel : `str` or None, default None
          y-axis label
      title : `str` or None, default None
          Plot title. If None, default is based on axis labels.
      color : `str`, default "rgb(32, 149, 212)" (light blue)
          Line color
      showlegend : `bool`, default True
          Whether to show the legend
  
      Returns
      -------
      fig : `plotly.graph_objects.Figure`
          Interactive plotly graph of the value against time.
  
          See `~greykite.common.viz.timeseries_plotting.plot_forecast_vs_actual`
          return value for how to plot the figure and add customization.
  
      See Also
      --------
      `~greykite.common.viz.timeseries_plotting.plot_multivariate`
          Provides more styling options. Also consider using plotly's `go.Scatter` and `go.Layout` directly.
      """
      # sets default x and y-axis names based on column names
      if xlabel is None:
          xlabel = x_col
      if ylabel is None:
          ylabel = y_col
  
      y_col_style_dict = {
          y_col: dict(
              name=y_col,
              mode="lines",
              line=dict(color=color),
              opacity=0.8,
          )
      }
      return plot_multivariate(
          df,
          x_col,
          y_col_style_dict,
          xlabel=xlabel,
          ylabel=ylabel,
          title=title,
          showlegend=showlegend,
      )
  
imports: import warnings
  import numpy
  import pandas
  import plotly.graph_objects
  from plotly.colors import DEFAULT_PLOTLY_COLORS
  from plotly.subplots import make_subplots
  from greykite.common import constants
  from greykite.common.features.timeseries_features import build_time_features_df
  from greykite.common.logging import LoggingLevelEnum
  from greykite.common.logging import log_message
  from greykite.common.python_utils import update_dictionary
  from greykite.common.viz.colors_utils import get_color_palette
  from greykite.common.viz.colors_utils import get_distinct_colors
label_desc: Use image node_id 3 for calling a global function with example usage: plot_univariate(df, x_col, y_col, xlabel, ylabel, title, color, showlegend) and returns: plot_multivariate