For customizing theme goto config/theme/themeVariable.js and customize the variables according to your necessity. StrikingDash is based on antd.
For additional changes, here is the list of available variable for customization https://github.com/ant-design/ant-design/blob/master/components/style/themes/default.less

Using theme variables in the app.

Change font

Simplest way to change font is to go to google fonts, select fonts, click embed copy the link. Now goto public/index.html and paste the link in head tag. Please remove the links of any unused fonts from the head.

Now goto config/theme/themeVariable.js and set `font-family` variable

Sidebar & Topbar Dark/Light Layout

To change the sidebar and topbar layout background to dark, go to src/config/config.js and just set the darkMode to true. Else set false to keep the white background

import { theme, darkTheme } from './theme/themeVariables';

const config = {
  darkMode: false,
  rtl: false,
  theme,
  darkTheme,
};

export default config;
                                                    

Side Navbar & Top Navbar Layout

To change the Navbar side to top, go to src/config/config.js and just set the topMenu to true. Else set false to keep Navbar on Sidebar. You can update your menu item from src/layout/TopMenu.js For Top Navbar and src/layout/MenuItem.js for Side Navbar

import { theme, darkTheme } from './theme/themeVariables';

const config = {
    darkMode: false,
    topMenu: false,
    rtl: false,
    theme,
    darkTheme,
};

export default config;
                                                        

Change Logo

To change both dark and light logo, go to src/layout/withAdminLayout.js and change source of the logo image

<Link className="striking-logo" to="/admin">
    <img
    :src="!darkMode ? require(`@/static/img/Logo_Dark.svg`) : require(`@/static/img/Logo_white.png`)"
    alt="logo"
    />
</Link>
                                                            

RTL Setup

To change the layout to RTL set the rtl to true and change the dir to rtl from public/index.html

import { theme, darkTheme } from './theme/themeVariables';

const config = {
    darkMode: false,
    rtl: false,
    theme,
    darkTheme,
};

export default config;