Changing colour of fonts

Hi there,

I would like to change the colour of the font in the photo provided. I can not find a straightforward way of doing it. Where is the code I need to change to get these fonts in black?
I would like to change the colour of, (1) the navigation menu at the top right, (2) the main header text colour, (3) colour of the border around the boxes (as shown in the photo).

As always thank you very much,

Hello Ed,

Add this CSS code to Appearance > Customize > Additional CSS from dashboard.

    /* Menu color */
    @media only screen and (min-width: 1025px) {
      .main-navigation > li > a {
        color: #000;

    /* Header text color */
    .header-text {
      color: #000;

    /* Header button border color */
    .header-button {
      border-color: #000;